Ionic Liquids In Aqueous Media Research Articles

New insight into molecular interactions of surface-active ionic liquid (SAIL) with some biomolecules: Experimental and computational approaches

Understanding the influence of ionic liquids (ILs) on the solubility of biomolecules in aqueous solutions is crucial for designing and optimizing novel biotechnological processes. However, the molecular-level mechanisms underlying this influence remain inconclusive and not fully elucidated. To contribute toward the understanding of molecular interactions between amino acids and ionic liquid in aqueous media, measurements of the densities and speeds of sound for L-serine and glycyl-L-serine in (0.00, 0.005, 0.01, 0.03, and 0.05) mol·kg−1 aqueous solutions of 1-octyl-3-methylimidazolium bromide were conducted at T = (288.15, 298.15, 308.15, and 318.15) K. From experimental data various thermodynamics paramours such as apparent molar volume (Vϕ), the partial molar volume (Vϕ0), standard partial molar volumes of transfer (ΔVϕ0) partial molar isentropic compression (Kϕ,s) and partial molar isentropic compression of transfer (ΔKϕ,S0) have been examined. Along with experiment results, computational tools were also utilized for a deeper understanding of the molecular changes. From density functional theory (DFT), the highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) were calculated and utilized to obtain molecular descriptors such as ionization energy (I), electron affinity (A), hardness (η), softness (S), chemical potential (μ), and electronegativity (χ). Thermochemical properties, including change in enthalpy (ΔH), and change in Gibbs free energy (ΔG), were predicted. Molecular docking studies were used to analysis the molecular interaction of ionic liquid with I-Motif structure and structural changes.

Complete removal of organophosphate pesticides from wastewaters with sustainable ionic liquid-based aqueous two-phase strategy

Due to extensive food production, organophosphate pesticides (OPs) are widely utilized for crop protection, leading to their presence in the environment. The focus of this study was the design of an efficient aqueous biphasic system (ABS) strategy for OP removal, namely, malathion (MAL), azinphos-methyl (AZM), and chlorpyrifos (CHP) from water. Different ionic liquids (ILs) with symmetrical cations were selected as ABS phase-formers (tetrabutylphosphonium salicylate, tetrabutylammonium salicylate, 1,3-dibutylimidazolium dicyanamide, 1,3-dibutylimidazolium salicylate and 1,3-dibutylimidazolium bromide) with citrate salt as a salting-out agent. Initially, phase diagrams were determined, followed by partition studies revealing that the partition of MAL and CHP aligns with the IL- ABS formation trend, while the AZM partition is governed by specific interactions with ILs. For optimization studies, tetrabutylphosphonium-salicylate i.e. [TBP][Sal]-based ABS was chosen, due to obtained high extraction efficiencies of over 99.3 %. After establishing the effects of pH, temperature, tie-line length, and phase ratio on extraction performance, extraction of OPs from a real wastewater sample further confirmed the effectiveness of the designed method achieving complete removal of each pesticide. Furthermore, recovery of IL was achieved using an antisolvent method to precipitate CHP followed by IL-reuse in three consecutive cycles without efficiency decreased. Finally, it was demonstrated that [TBP][Sal] exhibits low cytotoxic potential, indicating that the presence of low amounts of this IL in aqueous media could be acceptable from ecotoxicological standpoint. This study showcased the exceptional potential of the proposed technology for the efficient and sustainable treatment of wastewater contaminated with OPs, affirming its capability to treat significant wastewater volumes.

Influence of an antibiotic drug neomycin sulphate on mixed micellization behavior of imidazolium based surface-active ionic liquids in aqueous media

Imidazolium-based surface-active ionic liquids (SAILs) have unique physicochemical features that make them ideal for biomedical applications. Because SAILs have a higher surface activity than conventional surfactants, they can improve drug permeability across biomembranes, making them superior drug carriers than existing solutions. In-depth studies of interactions prevailing in mixed micellar system of SAILs in the presence of drug are required to fully exploit the promise of these materials in drug delivery applications. Thus, various thermodynamic, mixed micellar and surface-active properties of two imidazolium-based SAILs with different cationic structures i.e.1-dodecyl-3-ethylimidazolium bromide [C12eim][Br] and 1-dodecyl-3-butylimidazolium bromide [C12bim][Br] have been determined in water and 5 mM neomycin sulphate solution in aqueous media. The study has been conducted for different mole fractions of mixed micellar system of SAILs using conductivity and surface tension measurement techniques. Various theoretical models such as Clint, Rubingh, Motomura and Rodenas models have been applied to understand the interactions prevailing in the mixed [C12eim][Br] /[C12bim][Br] system in water and neomycin sulphate solution in aqueous media.

Molecular Interactions of Diphenhydramine-hydrochloride with Some Imidazolium-Based Ionic Liquids in Aqueous Media at T = 293.15-313.15 K: Volumetric, Acoustic, and UV Absorption Studies.

From the density (ρ) and speed-of-sound (u) measurements, the interactions of the drug diphenhydramine-hydrochloride (DPH) with three imidazolium-based ionic liquids (ILs) (1-butyl-3-methylimidazolium chloride, [C4mim][Cl], 1-hexyl-3-methylimidazolium chloride1, [C6mim][Cl], and 1-methyl-3-octylimidazolium chloride, [C8mim][Cl]) have been investigated in aqueous medium at T = 293.15–313.15 K and experimental pressure p = 0.1 MPa. From the density calculations, the apparent molar volume (Vϕ) and the apparent partial molar volumes of transfer (ΔtVϕo) have been determined for various solutions of DPH in aqueous solutions of different ILs. In addition, from the speed-of-sound data, the apparent molar isentropic compressibility (Kϕ), apparent partial molar isentropic compressibility (Kϕo), and apparent partial molar isentropic compressibility of transfer (ΔtKϕο) have been calculated. The pair and triplet interaction coefficients are derived from apparent partial molar volumes of transfer. For the present mixtures, the absorption spectra have been also recorded using a UV–visible spectrophotometer. Using Hepler’s constant, the structure-making nature of the solute has been confirmed. All these calculated parameters provide detailed insights into various physicochemical interactions prevailing in the ternary system and confirm the presence of a strong attractive interaction between DPH and ILs.

Alterations induced in the micellization behavior of dioctyl sodium sulfosuccinate in the presence of imidazolium-based surface-active ionic liquids in aqueous medium

The present work describes the effect of 1-nonyl-3-methylimidazolium bromide [C9mim][Br] and 1-dodecyl-3-methylimidazolium bromide [C12mim][Br] on aggregation behavior of anionic surfactant dioctyl sodium sulfosuccinate (NaAOT) in aqueous medium by employing different techniques such as conductivity measurement, UV–Visible spectroscopy and FT-IR spectroscopy. The conductivity data of anionic surfactant in the aqueous solution of surface-active ionic liquids is taken experimentally in the temperature range from 293.15 to 308.15 K with the interval of 5 K at various concentrations that is, (0.04, 0.08, 0.12, and 0.16) wt.% of both the SAILs. The critical micelle concentration (CMC) of NaAOT is detected to alter in the presence of both the SAILs. Temperature dependence of CMC obtained from conductivity measurements is utilized to evaluate various thermodynamic parameters of micellization such as, standard free energy of micellization (), standard enthalpy of micellization (), and standard entropy of micellization (). The UV–Visible spectroscopic study is utilized to confirm CMC values obtained from conductivity measurements, which are found to be in good agreement. FT-IR Spectra are recorded to analyze the structural changes that prevailed in both systems.

Influence of tetra ethyl ammonium bromide (C2H5)4NBr on the aggregation behavior of surface active ionic liquid 1-tetradecyl-3-methylimidazolium bromide [C14mim][Br

In this work, we tend to explore the effect of organic electrolyte i.e. tetra ethyl ammonium bromide (C2H5)4NBr on the aggregation behavior of 1-tetradecyl-3-methylimidazolium bromide [C14mim][Br] by utilizing electrical conductivity measurement, refractive index measurement, UV–Visible spectroscopy as well as FT-IR spectroscopic study. First of all, the synthesis of [C14mim][Br] is carried out in the laboratory, then the critical micelle concentration (CMC) of [C14mim][Br] is determined using conductivity measurements at temperatures 298.15 K, 308.15 K and 318.15 K in the absence and presence of (C2H5)4NBr at different concentrations 1 mM, 2 mM and 5 mM. The reduction in value of CMC is observed with respect to increasing concentration of (C2H5)4NBr and with the increase in temperature, the value of CMC also increases. These results are observed due to the establishment of reinforced hydrophobic interactions between the hydrophobic parts of surface active ionic liquid and the electrolytes. Then we reflected different thermodynamic parameters such as, standard free energy of micellization (ΔGm0), standard enthalpy of micellization (ΔHm0), and standard entropy of micellization (ΔSm0) in the temperature range 298.15 K–318.15 K, utilizing the value of CMC obtained from conductivity measurements. A graphical contrast of these thermodynamic parameters has been made. Further refractive index measurement and UV–visible spectroscopic study have been employed to verify the CMC obtained using conductivity measurement, which is found to be very close to that obtained via conductivity study. The alterations produced in the respective system have been confirmed via FT-IR spectroscopic study, which signify the variations produced by electrolyte on the aggregation of surface active ionic liquid in aqueous media.

Induced Alterations in the Aggregation Behavior and Thermodynamic Properties of Anionic Surfactant Sodium Tetradecyl Sulfate (STS) in presence of Imidazolium Based Ionic Liquid in Aqueous Media: A Conductometric Study

Surfactants can be considered as an important class of chemical species having a polar head and non-polar tail, which make it capable to be utilized in many industrial formulations such as coatings, paints, lubricants, and cosmetics, etc. Also, ionic liquids, which are actually molten salts, are also having many useful properties such as negligible vapor pressure, high thermal stability, etc. They can modify the physiological as well as aggregation properties of conventional surfactants according to our desire. The mixtures of ionic liquids with a surfactant are found to be better systems for many industrial applications than individual ones. Thus the micellization behavior of sodium tetradecyl sulfate STS is investigated in the presence of 1-propyl-3-methylimidazolium bromide [C3mim][Br] in aqueous media. For this, ionic liquid 1-propyl-3-methylimidazolium bromide [C3mim][Br] is synthesized in our lab. Then the conductivity measurement is done to determine the critical micelle concentration (CMC) of sodium tetradecyl sulfate STS in the absence and presence of (0.02, 0.05 and 0.1) wt. %, of 1-propyl-3-methylimidazolium bromide [C3mim][Br] in aqueous medium at three different temperatures i.e. (298.15, 303.15 and 308.15) K. The results are then utilized to find the thermodynamic parameters of micellization such as, standard free energy of micellization, standard enthalpy of micellization, and standard entropy of micellization, which are important to understand the driving force behind the process of micellization.

Self-Organization of Cationic Surfactant in Hydrophilic Ionic Liquid in Aqueous Media at Various Concentrations

The present work focus on the study of thermodynamical parameters of micellization of surfactant in the presence of altered concentrations of the ionic liquid. The conductivity measurement has been done to study the aggregation behavior of mixed system of SDS and ionic liquid [C3mim][Br] at various concentrations (0.04, 0.08 and 0.12 weight percent of IL) and temperatures break reserved for 5K from 298.15 K - 308.15 K. The measured data of conductivity have been employed to know the CMC. Thermodynamical parameters of aggregation such as standard Gibb’s free energy of micellization, standard enthalpy and entropy of micellization determined and discussed. Outcomes have been elucidated in terms of the impact of IL on the micellization process of the sodium dodecylsulphate.

Antimicrobial Colloidal Complexes of Lysozyme with Bio-Based Surface Active Ionic Liquids in Aqueous Medium.

Bio-based surface-active ionic liquids (SAILs) have been synthesized and investigated for their complexation with lysozyme (LYZ) in an aqueous medium to develop antimicrobial SAIL-LYZ colloidal complexes. The synthesized SAILs, [Cho][Sar] and [Cho][Doc], are comprised of choline ([Cho]+) and lauryl sarcosinate ([Sar]-) or deoxycholate ([Doc]-). The constituent anions of the investigated SAILs are structurally dissimilar and thus resulted in contrasting complexation behavior toward LYZ, as suggested by the results obtained from different techniques. The interfacial behavior is monitored using tensiometry. Zeta-potential, turbidity, and dynamic light scattering results provide insights into the complexation phenomenon in bulk. The observations made from fluorescence and circular dichroism (CD) spectroscopy give information about the alterations in the inherent structure of LYZ. The thermodynamics of the binding of SAILs with LYZ is monitored using isothermal titration calorimetry (ITC). Computer simulations have been utilized to determine the preferential binding site of SAILs on LYZ, which supports the results obtained from different techniques. Interestingly, LYZ complexed with the investigated SAILs, which are non-antimicrobial, is found to exhibit enhanced antimicrobial activity depending upon the concentration regime of the used SAIL. In this way, we have developed new antimicrobial colloidal complexes of SAILs and LYZ. The present study provides useful insights to synthesize new bio-based SAILs to be utilized for creating colloidal formulations applicable in enzyme/protein stabilization, storage, and other biomedical applications.

Thermodynamics and micellization behavior of ethanolammonium carboxylate surface active ionic liquids in aqueous media

A systematic experimental study of the micellization of ethanolammonium carboxylate surface active ionic liquids (SAILs) in aqueous solutions was performed. The effect of two separate anions having different alkyl chain length, laurate and palmitate on the micellization behavior was studied. The effect of different cationic head groups, n-butyl, tertiary butyl as well as phenyl group on the micellization parameters was also investigated. The critical micelle concentration (cmc) values and the surface active parameters were evaluated from tensiometric methods. The values of cmc are observed to be lower for palmitate anion SAILs in comparison to the laurate anions. The values of surface tension reduction (πcmc) and surface excess (Γmax) show considerable variation as the anion chain length and the cationic head groups changed. The thermodynamics of the micellization parameters, standard Gibbs free energy of micellization (∆Gm°), enthalpy of micellization (∆Hm°) and entropy of micellization (∆Sm°) were evaluated by conductometric measurements. Using pyrene as a probe molecule, the cmc values were evaluated by steady state fluorescence. The values of critical micelle concentration obtained from three different methods for all the studied SAILs are found to be in good match with each other. The order of cmc for the synthesized SAILs were as follows: [NPEA][PAL] < [TBEA][PAL] < [NBEA][PAL] < [NPEA][LAU] < [TBEA][LAU] < [NBEA][LAU].

Hydrophobically Driven Morphologically Diverse Self-Assembled Architectures of Deoxycholate and Imidazolium-Based Biamphiphilic Ionic Liquids in Aqueous Medium.

Biamphiphilic ionic liquids (BAILs) having amphiphilic cation and anion are thought to exhibit improved surface activity and colloidal stability to be utilized in different applications. For their effective use, a control over synergetic hydrophobic and electrostatic interactions between oppositely charged ions along with the possibility of tuning of hydrophobicity of the core of aggregates is required. Focusing on this, new BAILs comprising a bile salt anion, deoxycholate, [DC]-, and 1-alkyl-3-methylimidazolium cations, [C nmim]+ ( n = 2, 4, 6, 8, and 12), were synthesized and characterized for their behavior at air-solution interface as well as in bulk. The synthesized BAILs exhibit high surface activity and self-assemble in the form of different architectures ranging from nanosheets (NSs), nanorods, and vesicles with varying hydrophobicities of the formed core of aggregates, depending on the length of alkyl chain of [C nmim]+. Analysis of various parameters obtained from investigated techniques suggested the changing role of [C nmim]+ from a counterion ( n = 2 and 4) to a cosurfactant ( n = 8 and 12) via a borderline case of [C6mim]+. This changeover in the nature of counterion controlled by hydrophobicity of alkyl chain resulted in morphological diversification in self-assembled architectures via varying set of interactions. It is believed that the present work would offer new perspectives in the self-assembly phenomenon of surfactants in general and surface active ionic liquids in particular to devise new strategies for inducing morphology-dependent functionality in self-assembled structures of BAILs.

Binary Mixtures of Ionic Liquids in Aqueous Solution: Towards an Understanding of their Salting-In/Salting-Out Phenomena.

The order of the salting-in or salting-out inducing ability of ions on the aqueous solubility of macromolecules in aqueous solutions is known as the Hofmeister series. Taking into account that ionic liquids (ILs) are constituted by ions, they can exert similar effects on the solubility of other ILs in aqueous media. In order to expand the knowledge on the salting-in/-out ability of ILs, experimental studies on the solubility of 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonylimide) in water in presence of other IL/salts were conducted at 298.15 K at atmospheric pressure. Both the impact of the anion and cation of the IL were evaluated with the following ILs/salts: 1-butyl-3-methylimidazolium chloride, 1-butyl-3-methylimidazolium hydrogensulfate, cholinium bis(trifluoromethylsulfonyl)imide, 1-butyl-1-methylpyrrolidinium bis(trifluoromethylsulfonyl)imide and lithium bis(trifluoromethylsulfonyl)imide, in a wide composition range. As happens with common salts, both salting-in and salting-out effects exerted by ILs were observed, with a higher impact exerted by the IL anion on the salting-out phenomenon. These data allow to better understand the ILs impact when designing liquid-liquid separation processes.

Synthesis, Characterization, Solution Behavior, and Density Functional Theory Analysis of Some Pyridinium‐Based Ionic Liquids

AbstractSome picolinium ionic liquids (IL) [α/γ‐PicC n][Br/NO3] (n = 3, 5, 7) were synthesized and characterized by 1H NMR data. The surface tension and density of all the IL were determined. The aggregation behavior of these IL in aqueous medium and in dichloromethane was assessed from the variation of electrical conductivity in these media. The critical aggregation concentrations of these IL in aqueous medium were found to decrease significantly by the addition of cetyltrimethylammonium bromide. The structural features and the conformation of these IL were further investigated by using density functional theory calculations. The bromide ion was found to be inclined asymmetrically to one side of the pyridinium nucleus, while the nitrogen of the nitrate group lies close to the nitronium ion of the pyridinium nucleus.

Characterization of interactions between β-lactoglobulin with surface active ionic liquids in aqueous medium

The interaction of β-lactoglobulin (βLG) with surface active ionic liquids (ILs), 1-dodecyl-3-methylimidazolium bromide [C12mim][Br] and 1-hexyl-3-methylimidazolium dodecylsulfate [C6mim][C12OSO3] has been investigated employing tensiometry, conductivity, fluorescence, dynamic light scattering (DLS), zeta potential and circular dichroism (CD) methods. A significant difference was observed in the nature of interactions present in the βLG-[C12mim][Br] system as compared to βLG-[C6mim][C12OSO3]. The IL, [C12mim][Br] interacted strongly with βLG to form complexes at the interface as compared to weaker interactions observed in case of βLG-[C6mim][C12OSO3] system. The results of intrinsic fluorescence measurements along with CD measurements have provided insights into the unfolding of βLG due to binding of ILs. Turbidity measurements have shown the coacervate formation in case of βLG-[C12mim][Br] which was also supported from DLS and zeta potential measurements. An excellent correlation of results obtained from multiple techniques has been used to characterize the interactional behavior of ILs and βLG in a wide concentration regime. The results of the present studies are expected to contribute in understanding the interactional behavior of βLG with surface active ILs and its effect on functionality of protein.

Studies on Micellar Behavior of PEO‐PBO or PEO‐PBO‐PEO Copolymers, or Surface Active Amphiphilic Ionic Liquids in Aqueous Media and Exploration of the Micellar Solutions for Solubilization of Dexamethasone and its Delayed Release

AbstractThe aggregation behavior of a di‐ and tri‐block copolymers of type PEO‐PBO, PEO‐PBO‐PEO, surface‐active ionic liquid (SAIL) of type 4‐dodecyl‐4‐methylmorpholinium chloride [C12mmor][Cl], and 1‐dodecyl‐1‐methylpyrrolidinium chloride [C12mpyrr][Cl]) in water as well as in 10 mM of a poorly water soluble dexamethasone (dex) aqueous solution was studied by determining the critical micelle concentrations using drug solubilization, surface tension, and isothermal titration calorimetry (ITC) methods. ITC measurements were also made on solutions prepared by mixing the micellar aqueous solutions of copolymers and simple aqueous solutions of SAIL across the mole fractions at three different temperatures (298.15, 308.15, and 318.15 K). The thermodynamic parameters, namely Gibbs free energy (ΔGm), enthalpy (ΔHm), and entropy (ΔSm), of micellization were calculated, and it was observed that the negative ΔGm and positive ΔSm for the mixture solutions increase with the increase in mole fraction of SAIL. Otherwise, the micellization is reported to be a spontaneous and highly entropy‐driven process. The dex‐solubilized micellar solutions were mixed with agar to obtain standing gels. The gel samples were dry‐cast into thin films, and the release of dex from films by simple dilution was monitored by UV measurements. The drug release data was fitted to several mechanistic models, and it was inferred that the release mechanism for dex from thin films is non‐Fickian for mixtures and Fickian in copolymer or SAIL micellar aqueous solutions. The transport of dex is diffusion‐controlled with diffusivities of 5.8–12 × 10−11 m2 s−1 for copolymer micelles, 5–11 × 10−11 m2 s−1 for micelles of SAIL, and 3–14 × 10−11 m2 s−1 for the mixed micelles of copolymer and SAIL in aqueous media.

Unprecedented self-assembled architectures of surface-active ionic liquids in aqueous medium.

The formation of ultra-thin 2D crystalline nano-sheets, -spindles and -ribbons by self-assembly of benzimidazolium-based single-tailed surface active ionic liquids (SAILs) is observed for the first time. The nature of formed bilayer architectures is governed by the functionalization of alkyl chains of SAILs via an amide or ester moiety.

Modulations in surface and aggregation properties of non-ionic surfactant Triton X-45 on addition of ionic liquids in aqueous media

The effect of hydrophilic ionic liquids (ILs), 1-butyl-2,3-dimethylimidazolium bromide [bdmim][Br] and 1-butyl-3-methylimidazolium bromide [bmim][Br] on the aggregation and surface active properties of non-ionic surfactant, Triton X-45 (TX-45) has been investigated in aqueous media. The surfactant properties such as critical micelle concentration (cmc), aggregation number (Nagg), surface and adsorption parameters were determined by surface tension and fluorescence techniques in TX-45+IL/water systems. The cmc values were found to be varying at different wt% of IL than in water. The cmc value of TX-45 slightly decreases at lower (0.1) wt% of IL [bdmim][Br] in the medium. In general, with increasing concentration of both ILs in the solution the cmc of surfactant solution increases, thus the surface activity decreases. The surface activity is much lower in aqueous TX-45/IL than in water. The IL [bmim][Br] is found to increase the cmc of surfactant more rather than IL [bdmim][Br]. The aggregation number of aqueous TX-45 solution decreases with increase in wt% of IL. The hydrogen bonding interactions prevailed in presence of IL [bmim][Br] than IL [bdmim][Br], this led to better solubilisation of surfactant monomers in the former. It is demonstrated that ILs [bdmim][Br] and [bmim][Br] can be judiciously used at different wt% for modifying the aggregation properties of TX-45.

A Green and Efficient One‐Pot Pseudo‐Five‐Component Reaction for Synthesis of Bis(pyrazol‐5‐ol) Derivatives via Tandem Cyclocondensation‐Knoevenagel–Michael Reaction

AbstractA simple, green and efficient approach for one‐pot pseudo‐five‐component synthesis of the 4,4’‐(arylmethylene)bis(1H‐pyrazol‐5‐ol) derivatives from hydrazines, dialkyl acetylenedicarboxylats/β‐ketoesters and aromatic aldehydes catalyzed by Dabco‐base ionic liquids in aqueous media has been successfully developed. All the reactions were performed under 3 mol% of ionic liquid catalyst, and afforded the corresponding bis(pyrazol‐5‐ol)s in excellent yields (81‐98 %). This method also offers several other notable advantages, such as environmental friendliness, short reaction times, easy workup and reusability of the inexpensive catalyst.

Assembly of Amphiphilic Hyperbranched Polymeric Ionic Liquids in Aqueous Media at Different pH and Ionic Strength

We demonstrated the assembly of amphiphilic hyperbranched protic ionic liquids (HBP-ILs) based on aliphatic hyperbranched polyester (HBP) in aqueous media in a wide range of pH and ionic conditions. The series of new branched polyionic liquids with different terminal groups, HBP-ILs, was synthesized by neutralization of carboxylic and sulfonic terminal acid groups of hypebranched core with N-methylimidazole (Im) and 1,2,4-1H-triazole (Tr). HBP-IL compounds with triazole and imidazole counterions form 12–16 nm core–corona micelles at pH 11.6. We found that the introduction of long hydrophobic terminal groups such as n-octadecylurethane tails to initial hydrophobic HBP core has larger effect on the size of micellar assemblies than the introduction of ionic terminals groups. Furthermore, tuning the hydrophilic/hydrophobic balance of HBP-ILs can be achieved by changing the degree of ionization of terminal groups and counterions by reducing pH from 11.6 to 5.2 or ionic strength to 0.1 M. These changes caused t...

Surfactant and Gelation Properties of Acetylsalicylate Based Room Temperature Ionic Liquid in Aqueous Media.

An amphiphilic room temperature ionic liquid (RTIL) containing acetylsalicylate anion of type 1-dodecyl-1-methylpiperidinium acetylsalicylate, [C12mpip][AcSa], is synthesized from the precursor [C12mpip][Cl] by an ion exchange process. The sample is characterized, and its surface active and aggregation behavior in water has been studied and explained. The critical aggregation concentrations (CACs) are determined by a variety of methods, namely, electrical conductivity, surface tension, steady state florescence, and isothermal titration calorimetry (ITC) at different temperatures. As compared to its precursor, [C12mpip][AcSa] has low CAC values, indicating enhanced favorable interactions between the [alkylmpip]+ cation···bulky [AcSa]- anion and also hydrogen bonding of both of the ions with water. The free energy of aggregation ΔG0a is always negative, and both enthalpy and entropy of aggregation drive the aggregation process. The micelle-like aggregates are ellipsoidal in shape. The aggregation numbers are determined from translational diffusion coefficients and florescence quenching measurements. Aggregates of [C12mpip][AcSa] are larger than those of its precursor IL with chloride anion. Therefore, it is evident that the close interactions between the ion pairs of [C12mpip]+···[AcSa]- facilitate packing of more molecules in an aggregate. The steady state and oscillatory rheology measurements in aqueous solutions consisting of mixtures of [C12mpip][AcSa] and sodium salicylate (SS), an hydrotope additive, were carried out. The analysis of zero shear viscosity and moduli properties as a function of concentration and temperature reveals that the addition of SS promotes the growth of small ellipsoid aggregates into large worm-like structures with a typical viscoelastic gel behavior. The moduli properties vs temperature profiles are complex and no hysteresis was produced in heating and cooling modes, suggesting the thermoirreversibile and complex nature of the network structures. The release of the acetylsalicylate anion from the gels could be triggered by simple dilution, and the release occurs due to surface erosion and demicellization.